/*
 * Copyright 2016 The BigDL Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intel.analytics.bigdl.dllib.nn

import com.intel.analytics.bigdl.dllib.nn.abstractnn.{Activity, AbstractModule}
import com.intel.analytics.bigdl.dllib.tensor.TensorNumericMath.TensorNumeric

import scala.reflect.ClassTag

/**
 * Identity just return the input to output.
 * It's useful in same parallel container to get an origin input.
 */
@SerialVersionUID(- 8429221694319933625L)
class Identity[T: ClassTag]()
  (implicit ev: TensorNumeric[T]) extends AbstractModule[Activity, Activity, T] {

  override def updateOutput(input: Activity): Activity = {
    output = input
    output
  }

  override def updateGradInput(input: Activity,
    gradOutput: Activity): Activity = {

    gradInput = gradOutput
    gradInput
  }
}

object Identity {
  def apply[@specialized(Float, Double) T: ClassTag]()
      (implicit ev: TensorNumeric[T]) : Identity[T] = {
    new Identity[T]()
  }
}
